Devices for aerating, spraying, pumping, mixing, and developing the flow of liquids are well known in the art. Such devices are frequently used, for example, to treat or condition liquids contained in a reservoir such as a pond, a lake, a lagoon, a canal, a tank, a waste treatment basin, or the like. Aerators, in particular, are commonly used to enrich the oxygen content of water by pumping it upwardly into the air. Aerators are also used to scrub undesirable gases from liquids and to cool large quantities of liquids for future recirculation. Mixers and flow developers, in contrast, do not pump or spray liquids into the air. Instead, they circulate a body of liquid beneath its top surface. In this way, mixers and flow developers are commonly used, for example, to blend different types of liquids together and to agitate biological or other solids that are suspended in a liquid.
Many devices of this type are designed to float on the top surface of a liquid. Such floating devices include an impeller attached to a rotatable shaft, a motor for rotating the shaft, and a buoyant float for supporting the motor relative to the top surface of the liquid. When the impeller is rotated by the motor, liquid is either pumped into the air (in the case of aerators), or circulated below its surface (in the case of mixers and flow developers). In either event, the motor is either arranged on the float (as a non-submersible or partially-submersible motor), or beneath the float (as a fully-submersible motor). Floating aerators, mixers, and flow developers are disclosed, for example, in U.S. Pat. Nos. 3,416,729 (Ravitts et al.), 3,606,273 (Johnson), 3,856,272 (Ravitts), and 4,089,620 (Ravitts).
Other devices of this type are statically arranged on the bottom surface (or floor) of the liquid filled reservoir. Such stationary devices include an impeller attached to a rotatable shaft, a motor for rotating the shaft, and a stand for supporting the motor relative to the bottom surface of the liquid body. Of course, the motor of such stationary devices is fully-submersible.
In both floating and stationary devices, certain precautions must be taken in order to prevent liquids from invading, entering, and damaging the motor. In most instances, a submersible seal fabricated from a hard and insoluble material (e.g., silicon carbide or tungsten carbide) is disposed between the motor and the shaft in order to seal and protect the motor from leakage. Although effective for relatively short durations, such seals suffer from many noted deficiencies including, but not limited to: (1) a susceptibility to friction and corrosion; (2) a tendency to wear and leak; (3) a propensity to freeze-up in icy conditions; (4) a need for frequent servicing and/or replacement; and (5) a high relative cost.